Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle- or large-sized devices, such as vehicles, use a middle- or large-sized battery module having a plurality of battery cells electrically connected with each other because high power and large capacity are necessary for the middle- or large-sized devices.
Preferably, the middle- or large-sized battery module is manufactured with small size and weight if possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle- or large-sized battery module. Especially, much interest is currently generated in the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the weight of the pouch-shaped battery is small, the manufacturing costs of the pouch-shaped battery are low, and it is easy to modify the shape of the pouch-shaped battery.
For the middle- or large-sized battery module to provide power and capacity required by a predetermined apparatus or device, it is necessary for the middle- or large-sized battery module to be constructed in a structure in which a plurality of battery cells are electrically connected in series with each other, and the battery cells are stable against an external force.
Also, the battery cells constituting the middle- or large-sized battery module are secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from the high-power, large-capacity secondary battery during the charge and discharge of the battery cells. If the heat, generated from the unit cells during the charge and discharge of the unit cells, is not effectively removed, the heat accumulates in the respective unit cells, and therefore, the deterioration of the unit cells is accelerated. According to circumstances, the unit cells may catch fire or explode. For this reason, a cooling system is needed in a battery pack for vehicles, which is a high-power, large-capacity battery.
In a middle- or large-sized battery pack including a plurality of battery cells, on the other hand, the deterioration of the performance of some battery cells leads to the deterioration of the performance of the battery pack. One of the main factors causing the nonuniformity of the performance is the nonuniformity of cooling between the battery cells. For this reason, it is required to provide a structure to secure the uniformity of cooling during the flow of a coolant.
Especially, in the middle- or large-sized battery pack, the vertical sectional area of a duct at a coolant inlet port side (hereinafter, referred as an ‘inlet port’) and a duct at a coolant outlet port side (hereinafter, referred as an ‘outlet port’) has a great influence on the coolant flux distribution in the battery pack.
Generally, if the vertical sectional area of the inlet port is greater than or equal to that of the outlet port, a relatively large amount of coolant is introduced into a channel between the battery cells near the coolant inlet port, whereas a relatively small amount of coolant is introduced into a channel between the battery cells far away from the coolant inlet port, with the result that it is difficult to accomplish the uniform cooling between the battery cells.
As a technology for solving the problem caused due to the nonuniform distribution of the coolant, a technology for improving the cooling efficiency by the provision of a structure in which a communication member is provided at a coolant inlet port and a coolant outlet port of a battery module, and the communication member includes a first connection channel (inlet duct) and a second connection channel (outlet duct) is disclosed in Korean Patent Application Publication No. 2006-037625. According to the disclosed technology, the sectional area of the channel between the battery cells increases as the channel becomes more distant from the coolant inlet port, thereby partially accomplishing cooling uniformity. However, the vertical sectional areas of the first and second connection channels are the same, and therefore, a large amount of coolant is driven into the channel between the battery cells near the coolant inlet port. As a result, it is not possible to thoroughly accomplish the uniformity of cooling between the battery cells.
Consequently, there is a high necessity for a technology to fundamentally solve the above-mentioned problems.